RABIES IN KUDUS: WHY, WHAT ARE THE IMPLICATIONS TO THE GAME INDUSTRY AND WHAT CAN BE DONE? by Dr Ulf Tubbesing, veterinarian, game rancher and game dealer February 2016 INTRODUCTION Following the ongoing outbreak of rabies in Namibia (especially in Kudus), I have received numerous requests for more information regarding this disease, its risk to man, the kudu population at large and possible steps to be taken to curb the disease. In spite of rabies being a well-known and much researched disease, many uncertainties exist around the peculiar, seemingly Namibia specific, manifestation of rabies decimating our Kudu and Eland populations country wide. BACKGROUND Rabies, a fatal viral disease known since ancient times, attacks the central nervous system (brain and spinal cord) of all mammal species, including man. This disease occurs sporadically, virtually throughout the entire world but is endemic (occurs commonly and widespread) to Namibia, with a high prevalence in the central and northern regions. In recent years the disease also occurred in the southern and eastern parts of the country. Rabies is known as a disease with a low morbidity (low number of animals in a population affected) and near 100% mortality amongst infected animals. However, the Namibian rabies situation is unique, where it seems that the disease spreads from Kudu to Kudu (and Eland to Eland) and reaches epidemic proportions with devastating effects in these species. ARE KUDUS REALLY DYING OF RABIES OR IS THIS SOME KUDU PEST? There appears a great deal of confusion regarding the cause of death amongst Kudus in Namibia. Many farmers are sceptic to the diagnosis of rabies and prefer talking of the Kudu pest. Even though the clinical signs shown by Kudu/Eland suffering from rabies are suggestive of the disease, they are by no means diagnostic. However, the Central Veterinary Laboratory in Windhoek has examined the brains of many Kudus with a rabies specific test (Immuno-fluorescent Antibody test) and found a great number testing positive, thus leaving no doubt that this is an outbreak of rabies. A similar outbreak occurred in 1977-85, causing severe mortality amongst the country s Kudu population. I personally observed how this disease, within months, diminished the once very abundant Kudu population on our farm near Windhoek to a mere fraction of its original number. 1
DISEASE TRANSMISSION In the vast majority of cases the rabies infection starts with an animal being bitten by an infested animal (Jackal, yellow Mongoose, dog etc.). The bite wound is contaminated with virus particles contained in the attacker s saliva. The virus then migrates up the nerves towards the spinal cord and eventually the brain, where it preferentially infects and multiplies in certain areas of the brain, resulting in rather predictable symptoms (see below). From here the virus migrates down the nerve tracts to the salivary glands, where another phase of rapid viral replication occurs, resulting in very high concentration of virus being excreted in the saliva, rendering this animal infectious to other animals. Detectable levels of virus have been noted in the saliva of infected animals from a few days before the onset of symptoms up until (or just before) death. As a general rule it can Figure 1: Kudus are social browsers. be said that the closer an infectious bite is to the head of an animal, and the more severe the bite wound/s inflicted, the quicker and greater is the likelihood of the bitten animal (or man) succumbing to the infection. It may take up to one year from being bitten by a rabid animal before a patient may show clinical signs of rabies and then die. Even though some animal species play a more important role in the transmission of rabies (Jackal, yellow Mongoose, dog etc.) no known carrier state (i.e. animal species that can harbor and spread the virus without eventually dying from the disease) has yet been identified. This means that all infected animals will die within about 10 days from the onset of symptoms. Amongst browsers, Kudus appear to be most susceptible to rabies, likely followed by Eland. Within a Kudu population, rabies most probably starts with a Kudu being bitten by a rabid animal, however, the further spread of this disease is associated with the species susceptibility to the disease, its social behavior, where communal grooming as well as group feeding from the same bush or tree are very common. The habit of browsing on thorn bushes will obviously result in great numbers of small wounds to be found in a Kudu s mouth, which present ideal portals for infection. This most likely explains why the disease in Kudus hardly occurs in areas where broad leaved (thorn less) bush and trees comprise the dominant available browse (Fig. 1). Because the portal of infection (mouth) in Kudus is very close to both brain and 2
salivary glands, it appears logical that both the course of disease (infection to time of symptoms and death) and the spread of rabies within a Kudu population are far quicker and more dramatic than in most other species. In recent years, frequent reports of similar devastating outbreaks where rabies also decimated Eland populations have been reported. To the best of my knowledge no other browsers have yet been affected to any significant degree. All infectious diseases tend to spread easier and faster where susceptible animals are in close proximity to each other. This explains why the risk and incidence of rabies is vastly increased, at places and times where animals are concentrated in specific areas, e.g. large kudu population (as well as other species) converging around water sources in the dry (winter) seasons in Namibia. It also explains why gregarious animals like Kudu, are so severely affected. A question commonly asked by sceptics is: If all these Kudus are dying from rabies why don t we see so many rabies cases amongst our predators? A rabid Kudu is not likely to chase after, nor able to bite a predator to transmit the disease. Further, because the virus is very labile (loses infectivity shortly after the host dies) the risk of transmission from dead Kudu to scavenger or predator is rather remote. Most of the carnivores remaining on commercial farmland tend to occur as solitary animals or in small groups, making them less susceptible to an outbreak of rabies within that species. However, cases have been reported where, in nature reserves, entire groups of social carnivores like wild dogs, bat eared foxes, lions etc. have been wiped out by the disease. SYMPTOMS IN ANIMAL INFECTED WITH RABIES Figure 2: Tame Kudu cow in close proximity to human settlement and seemingly oblivious to the presence of dog or man. The Kudu displays a high stepping and staggering gait. One of the first signs of this disease is unusual behavior displayed by the animal. Domestic animals often seem to become wild, showing unexplained aggression whereas wild animals become tame, literally straying into towns, gardens and homes thus increasing the risk of exposure of domestic animals and man (Fig. 2). Any animal showing abnormal behavior, especially if associated with other nervous signs (staggering, hindquarter paralysis, restless, drooling saliva or having difficulty swallowing, biting at objects real or imaginary, changed tone of voice with abnormal and continuous howling or bellowing) should be suspected of having rabies. All cat 3
species as well as the honey badger tend to become extremely aggressive and vicious, resulting in severe unprovoked attacks on humans (e.g. the well-publicized attack by a rabid Cheetah on a farmer a few years ago). Infected animals lose the ability to swallow, which results in the excessive salivation (drooling) commonly noted. The animals also rapidly loose condition due to dehydration and starvation and are then frequently found in close proximity to water (Fig. 3), where they repeatedly make failed attempts at drinking, often make bellowing noises and eventually die an agonizing death. NOTE!! Excessive drooling and foaming at the mouth, the so called classic symptoms of rabies, are only displayed late in the disease and are not always present. These are also typical signs of animals having a foreign object (e.g. a bone) stuck in the mouth or gullet. Symptoms of rabies are frequently suggestive but never 100% diagnostic!! Starvation during a drought is a common reason for Kudus to penetrate into urban areas, especially at night, in search of food and water. This may easily be confused with rabies. Figure 3: This Kudu bull near a dam most likely succumbed to rabies. A disproportionally high mortality rate amongst mature Kudu bulls is often reported. In my experience the disease affects both bull and cow-calf herds equally, usually rapidly spreading and wiping out the entire affected group, however, mortalities in bulls are easier detected (e.g. a set of horns sticking out over grass level will be noticed on a game drive whereas a dead cow or calf would not be detected in high grass). ACTIONS TO MINIMISE THE EFFECT OF RABIES ON KUDUS/ELAND AND OUR BOTTOM LINE From a trophy hunting perspective the Kudu bull is both one of the most wanted and slowest maturing (i.e. reaching trophy standards only after 8-10 years or later) antelope. Needless to say, the decimation of the Kudu population due to rabies, especially on game fenced farms, poses a severe and long term threat to the farmer s income. Following the ecological route of letting nature run its course is not the wisest financial option available. The vaccination of Kudus against rabies appears a logical option. Oral vaccinations (putting out bait containing an oral rabies vaccine) were successfully performed on foxes in Europe, but are not feasible in Namibia. The bait and vaccine needs to be kept cold, something easily achieved in the European winter but not in Namibia. Research is currently being conducted to find a workable Namibian solution but, thus far no practical 4
and effective solution has been found for oral vaccination. Capture, vaccination and release programs were conducted in Canada (fox, skunk & raccoon) as well as in Arizona (skunk) and proved to be effective in curbing the spread of rabies in these countries. This is quite feasible for the vaccination of Kudu and Eland, especially in fully game fenced areas. With the aid of a helicopter an estimate of the Kudu population on a fenced farm is made. Kudus and Eland are then herded into a capture boma where, in the crush section, they are vaccinated and temporarily marked (water soluble paint blotch on the rump) to avoid the same animals being herded, captured and vaccinated twice. A much quicker and cheaper alternative is to literally dart vaccinate the animals form a helicopter (Fig. 4). Over the past few years we have done this repeatedly on a number of game farms both during and following an outbreak where the farmers reported an outbreak stopped within 10-14 days of vaccination. Those farms where we vaccinate annually or biannually now support a thriving Kudu/Eland population. This is cheaper, more effective and much quicker than the capture, vaccinate and release method mentioned above. Ideally one strives towards obtaining the highest possible percentage vaccine cover in the said Kudu population. However, a vaccination cover of 50-80% of free roaming dogs in urban areas Figure 4: Kudu bull seen from a helicopter. in SA and other countries proved to be efficient in curbing rabies outbreaks. Depending on the size of a farm, the Kudu population present and the % vaccination cover aimed for, such a vaccination campaign could be executed within a few hours at a cost equivalent to the trophy fee obtained for say 4-6 Kudu bulls shot. Spending this amount of money to protect and ensure a sustained healthy Kudu population on a given farm is definitely an economically feasible exercise. In cases where the resident Kudu population has already been decimated by the disease, vaccinating the residual population may be a costly exercise. As much helicopter time will be needed to fly and search the remaining few animals as would be needed to do a proper vaccination of the entire herd. Here it may be wiser and cheaper to introduce a sizeable group (ideally to more than double the current population on the farm thus indirectly achieving a 50% plus vaccine cover) of Kudus sourced from a rabies free area and vaccinated during capture. However, with the current scarcity of Kudu in Namibia restocking a farm would not be feasible. It has often been speculated that a game fence will substantially reduce the spread of rabies in Kudu. However, current experience proved that once an outbreak occurs within a fenced area, the fence may concentrate the effect of that outbreak. A further complicating factor on these farms is the fact that the normal migration routes have been cut, thus 5
drastically reducing the rate of resettlement by Kudus from outside the area and increasing the risk of inbreeding within the remaining kudu population should new breeding stock not be introduced. Rabies outbreaks are usually associated with high Kudu densities. As a result some advocate the radical thinning out of Kudus to reduce the risk of transmission and to minimize the financial impact on the farm. This approach may work on non fenced cattle farms that are not dependent on an income from the trophy hunt. However, during a culling operation it will be impossible to identify infected animals and one should keep in mind that meat from animals that suffered of infectious disease should not be used for human consumption. Remember that handling of a fresh rabies carcass may predispose people to the disease. Every precaution to avoid this must be taken. It is an unethical practice by both farmers and game dealers to knowingly capture and sell Kudus from a farm with an infected Kudu population in an attempt to reduce their Kudu numbers. HUMAN AND PET PRECAUTIONS TO BE TAKEN Even though the Namibian Veterinary Services suggest vaccination against rabies every 3 years, it is internationally accepted and recommended practice to, in endemic areas like Namibia, rather vaccinate all animals annually. You can further prevent pet exposure to rabid animals by securing your property to stop pets from straying. In problem areas, it is recommended that farmers vaccinate all their animals against rabies the human and animal risk as well as financial loss due to rabies infection in livestock is not worth taking. Inform your children, workers and neighbors about this disease. People should stay away from wild animals and unknown dogs, cats, etc. especially if these display abnormal behavior. Such animals should, if possible be examined by a veterinarian or be destroyed (do not shoot them in the head), and the head (wrapped in plastic to avoid virus contamination of the area and kept cool but not frozen!) submitted to the Central Veterinary Laboratory in Windhoek for a rabies test. Since the intensity of post rabies exposure treatment is determined by the associated risk to people, this is definitely essential if a person was bitten or had very close contact (e.g. wound contamination with saliva) with such an animal. People at high risk of exposure, e.g. farmers and their workers, veterinarians, etc. should seriously consider rabies vaccinations for themselves. WHAT SHOULD ONE DO IF EXPOSED? If your animal/s were in contact with an animal with suspected rabies, consult your veterinarian immediately. At the very least a rabies vaccination (even if your pet is current on its vaccinations) is indicated. If a bite was inflicted by a dog or cat not showing 6
symptoms suggestive of rabies and if the animal (both yours and the one inflicting the bite wounds) received regular rabies vaccinations, infection is highly unlikely. The virus is very sensitive to soapy detergents. People who were exposed to an animal suspected of suffering from rabies should immediately and thoroughly wash the skin and/or bite wounds with soap and water. This simple measure will drastically reduce the risk of contracting the disease. After this, call your doctor. Preventative treatment is safe and effective IF STARTED EARLY, however, no animal or person has ever survived the disease once symptoms of rabies set in. The treatment a person, bitten by a rabid animal is very expensive and is thus tailored to the certainty of the exposure (Was the animal involved rabies positive? What is the likelihood of rabies? Was it vaccinated? etc.). Wherever possible, submit the head of an animal suspected of having rabies for testing. The test is done free of charge. 7